1. Field of the Invention
The invention concerns optical filtering. Its applications include fibre optic telecommunication systems that transmit a plurality of streams of information simultaneously in the form of a spectral multiplex.
2. Description of the Prior Art
It is often necessary to be able to extract a selected one of the components of a multiplex of this kind. This requires an optical filter having the following properties:
high contrast between the transmission coefficients for optical waves in the passband of the filter and outside that band, and PA1 the facility to adjust the center optical frequency of that band.
Prior art devices utilize acoustic-optical interaction to implement these filters. They are described later. Unfortunately they do not have the above properties to a sufficient degree.
One object of the present invention is to provide a simple way to implement optical filters having these qualities to a greater degree than previously.